1. Technical Field
The present invention relates to a photomask, and to an exposure method that employs the photomask.
2. Related Art
An example of photomasks so far developed can be found in Japanese Laid-open patent publication No. H11-135402 (patent document 1). The photomask disclosed therein includes assist openings (opening features), in addition to a main opening. Here, the main opening refers to a transparent pattern provided so as to correspond to a predetermined opening pattern to be formed on a photoresist film over a semiconductor wafer, thus to be transferred thereto. The assist opening refers to a transparent pattern provided around the main opening, but not to be transferred to the photoresist film over a semiconductor wafer. The assist openings are aligned in a square grid pattern along with the main opening.